A technician quickly focused on the computer screen, where the words “multiple gunshots” appeared in large type. She listened to a recording of the shots — the tat-tat-tat-tat-tat of five rounds from a small-caliber weapon — and zoomed in on a satellite map to see where the gun had been fired: North 23rd Street in Milwaukee, 2,200 miles away.
At 7:23:48, the technician, satisfied that the sounds were gunshots, sent an alert to the Milwaukee Police Department. Less than two minutes later, or at 9:25:02 p.m. Wisconsin time, a tactical team arrived at the address to find five .22-caliber shell casings and a bleeding 15-year-old boy who had been shot in the arm. The casings, said Chris Blaszak, a detective assigned to the department’s intelligence fusion center, were found within 17 feet of where the alert had placed the gunman. Total elapsed time: 3 minutes, 55 seconds.
Milwaukee is one of an increasing number of cities around the country — just under 70 to date, including some in the New York area — that are using a gunshot detection system called ShotSpotter to pinpoint the location of gunfire seconds after it occurs. Last year, the company that developed ShotSpotter began offering a more affordable system, and that has brought in new clients and led other cities to consider trying it.
The detection system, which triangulates sound picked up by acoustic sensors placed on buildings, utility poles and other structures, is part of a wave of technological advances that is transforming the way police officers do their jobs.
In at least one city, New Bedford, MA., where sensors recorded a loud street argument that accompanied a fatal shooting in December, the system has raised questions about privacy and the reach of police surveillance, even in the service of reducing gun violence.
Gunshot Detectors: the ACLU’s view.
The Times has discovered that in at least one city, however, the system recorded a loud street argument. And the recording, which was made in New Bedford, MA., is likely to be at issue in the case against two men charged with murder.
It is not generally legal for law enforcement (or anyone else) to make audio recordings of conversations in which they are not a participant without a warrant. In addition to the apparently accidental eavesdropping reported by the Times, an important question is whether microphones can be remotely activated by police who want to listen to nearby conversations.
We’ll be watching closely to ensure that these systems don’t become the latest way for police to get around the Fourth Amendment. In New Bedford, MA., the district attorney told the Times he thought the recording could be admissible as evidence. If the courts start allowing recordings of conversations picked up by these devices to be admitted as evidence, then it will provide an additional incentive to the police to install microphones in our public spaces, over and above what is justified by the level of effectiveness the technology proves to have in pinpointing gun shots. It will also reduce the incentive of the manufacturers to design these systems so that they only pick up gunshots and not the conversations of people walking down the street.